Exploring the Association Between Apparent Diffusion Coefficient Values on Magnetic Resonance Imaging and the Response of Vestibular Schwannoma to Radiation

Introduction: With MRI diffusion weighted imaging (DWI), the apparent diffusion coefficient (ADC) measures the diffusion of water molecules within a tissue, and may predict the response of vestibular schwannomas (VS) to radiation. This study sought to investigate the association of pretreatment ADC values with tumor progression following radiation.

Methods: Performing a retrospective review at a single, tertiary care institution, patients with sporadic VS who were treated with gamma knife radiosurgery, had at least one pretreatment MRI with DWI with ADC values, and at least 12 months of posttreatment radiographic follow-up were identified. Demographic and clinical data were collected from the medical records. Three reviewers measured tumor diameter, tumor volume, and pretreatment ADC mean and standard deviations for all available MRI studies. Response to radiation was defined as a 20% reduction in tumor volume at last radiologic follow-up. Tumor progression was defined as either an increase in 2 mm in maximal tumor diameter or a 20% increase in tumor volume at last radiologic follow-up.

Results: A total of 27 patients with a sporadic VS treated with gamma knife radiosurgery met enrollment criteria. The cohort was composed of 52% women, with median age 67 years (range, 55–78). The median posttreatment follow-up was 36.8 months (range, 13.7–151.7). The median pretreatment maximum tumor diameter was 17.2 mm (range, 9.7–30.4) and the median pretreatment tumor volume was 0.83 cm³ (range: 0.19–5.4). A total of 66.7% of patients had a 20% reduction in tumor volume following radiation. The median ADC for responders was 1170.0 mm²/s (range 835.8–1771.6), compared with a median ADC for nonresponders of 1000.3 mm²/s (range 795.1–1423.1), which was not significantly different (p = 0.41). A total of 18.5% of patients demonstrated tumor progression at last follow-up following radiation. The median ADC of tumors that progressed was 1232.2 mm²/s (range 795.2–1313.7), compared with a median ADC of nonprogressing tumors of 1151.1 mm²/s (range 835.8–1771.6), which was not significant (p = 0.80). The median ADC was not significantly predictive of response or progression on univariate or multivariate logistic regression when controlling for age, gender, preradiation tumor greatest diameter, preradiation tumor volume.

Conclusion: While more patients will be included in the final analysis, currently in this cohort, the median ADC was not found to be predictive of radiation response or progression.

No conflict of interest has been declared by the author(s).